The erythropoietin receptor, a member of the hematopoietic cytokine receptor superfamily, is required for erythroid cell maturation. We have been studying the transcription control of the human erythropoietin receptor gene as representative of early events in erythropoiesis. Transcription analysis of the human erythropoietin receptor gene promoter identifies two critical elements for gene regulation: binding sites for transcription factors Sp1 and GATA-1 located within 50 bp of transcription initiation. The promoter assay is able to recapitulate the high and low activity of the endogenous gene activity in erythroid OCIM1 and K562 cells, respectively. While the erythropoietin receptor is known for its role in erythropoiesis, it has also been detected in non-hematopoietic tissues including brain which may also be related to expression in vascular endothelium. Analyses of erythropoietin receptor transcripts show that a number of spliced forms exist in fetal and adult brain. Mutiple clones corresponding to alternatively processed transcripts were isolated during screening of a human brain cDNA library. Sequencing revealed two clones derrived from an alternate initiation site located more than 20 kb 5' of exon 1. Examination of the erythropoietin receptor transcripts in non-erythroid cells suggests that these alternately initiated transcripts are expressed at a level of 10% or less compared with the erythroid form. These data indicate that both transcription and post-transcription processing regulate expression of the erythropoietin particularly in non-hematopoietic tissue. DNase I hypersensitivity will be used to determine the role of the alternate initiation site in hematopoietic and non-hematopoietic expression. These data also suggest that the erythropoietin receptor may function in other processes in addition to its role in erythroid cell development. To investigate the function in vivo of erythropoietin receptor expression in non-hematopoietic tissues, the erythropoietin receptor "knockout" mouse that die in utero due to anemia will be used to attempt selective rescue using an erythroid specific promoter.